This invention relates to a method and apparatus for cleaning and cooling high temperature corrosive synthesized gas and, more particularly, to such a method and apparatus utilizing a static regenerative hot gravel bed, and a fluidized bed of fine particles which is recirculated through a heat exchanger.
Several well-known techniques, such as the gasification of coal, are available for producing synthesized gas (hereinafter referred to as "syngas") which may be passed to a topping combustor and a gas turbine, or the like, for an integrated gas combined cycle (IGCC) system and second generation pressurized circulating fluidized bed (PCSB), or, alternatively, for use in chemical processes wherein synthetic hydrocarbons are manufactured. However, the syngas so produced often contains a relatively high quantity of corrosive gaseous species and acid pollutants, such as CO, HCl, NH.sub.3, H.sub.2 S and sulphur constituents generally, and, to a lesser extent, other corrosive gaseous species, alkali particles, and hydrocarbons (hereinafter referred to as "pollutants") which must be removed to comply with federal and state emissions standards.
Such pollutants are typically removed using a metal regenerative process in which pollutants in the syngas react with metal and are then regenerated producing elemental sulphur and chlorine. To enhance this pollutant removal process, the syngas is often initially cooled from temperatures which may exceed 2600.degree. F. This cooling may be effected using a conventional tube and shell heat exchanger arranged to be either convective or radiant. In a convective (or "fired tube") arrangement, syngas is passed through the tubes and a cooling medium (such as water) is passed through the shell around the tubes. Alternatively, in a radiant arrangement, syngas is passed through the shell and a cooling medium is passed through the tubes. A disadvantage with either method though is that each is prone to corrosion and pluggage caused by the presence of corrosive gases and a low melt eutectic of inorganic compounds.
Alternatively, syngas may be cooled and pollutants removed therefrom using a system incorporating a circulating fluidized bed with a spouting bed. This method calls for mixing and reacting syngas with fresh sorbent and a cooled recycle stream of sorbent. A disadvantage of this method is that it utilizes a grid, which is typically water-cooled, resulting in the condensation of acid gases which may then plug nozzles in the grid.